Certain printing systems use drop on demand ink jet printheads. These printheads deposit ink through one or more nozzles onto a substrate to create a desired image. For example, in some large-scale applications, ink jet printing systems have been used to print images on substrates, such as banners, museum displays, billboards, sails, and bus boards.
Typically, the ink used in these printing systems are made of a dye or pigment to create the various colors of the image, and a carrier liquid, such as water or some other suitable solvent. In addition, the ink contains a polymer that acts as a glue which fuses to a harden state to keep the pigment in place after the ink has been deposited onto the substrate.
However, over time, the ink accumulates in the nozzles, as well as around the orifices of the nozzle plates, and in the various channels of the printhead which convey the ink through the printhead to the nozzles.
Conventional techniques to clean the printheads include removing the printhead from the printing system, forcing a solvent such as glycol ether DPM acetate through the printhead, and then purging the printhead with high pressure air to blow out the debris from the channels and nozzles.
However, forcing glycol ether DPM acetate through the printhead has certain drawbacks. When glycol ether DPM acetate is streamed into the head, the fluid simply takes the easiest route through the printhead, thereby avoiding any blocked channels. The printheads are typically held together by an epoxy that can break apart if a chemical that is too aggressive is introduced, or if a pressure that is too high is used to force solvents or air through the printhead.
Glycol ether DPM acetate is commonly used in cleaning operations of printheads, which is not a very aggressive chemical. As such, glycol ether DPM acetate does not properly re-dissolve polymer that has been throughly dried. Furthermore, glycol ether DPM acetate tends to simply break the very dry polymer into chunks which can then flow into the smaller channels of the printheads, thereby exacerbating the problem. Thus, the use of glycol ether DPM acetate is typically effective if the printheads are still wet with ink or if used immediately after blockage is detected.
The present invention implements a method of cleaning ink jet printheads without rendering the printheads inoperative by soaking the printheads in a first cleaning solution of acetone and n-methyl-2-pyrolidone, and then flushing the printhead with a gas, such as air. The solution is made of about 70% acetone and about 30% n-methyl-2-pyrolidone.
In some embodiments, prior to soaking the printhead the printhead is flushed with a second cleaning solution, such as, for example, glycol ether DPM acetate, and an operator observes the streaming of the second cleaning solution from one or more nozzles of the printhead to determine if the printhead is partially or fully plugged. The printhead can also be flushed with the second solution after being flushed with the first cleaning solution. In some instances, the printhead is discarded if the printhead remains partially or fully plugged.
In certain embodiments, a print test is performed. If the print head passes the print test, it is typically returned to service. If not, then steps are taken to determine if the failure is due to an electrical malfunction. If the failure is attributable to an electrical malfunction, the printhead is disassembled to determine the cause of the electrical malfunction. If an electrical malfunction is not the cause of the failure of the print test, then the print head is again soaked in the first cleaning solution, and then flushed with air. If the print head still fails the print test, the printhead is typically discarded.
In some embodiments, the process of soaking the printhead in the first cleaning solution and then flushing the printhead with air is performed two to three times or more. The soaking process can occur over a time period of about 15 minutes, and the flushing process can occur over a time period of about 10 seconds. The gas can be at a pressure of about 5 psi.
In another embodiment, a method of cleaning a printhead includes soaking the printhead in a solution made of acetone and n-methyl-2-pyrolidine, flushing the printheads with a air, repeating the soaking and the flushing steps two additional times, flushing the printhead with a solution of glycol ether DPM acetate, and observing the streaming of the solution of glycol ether DPM acetate from the nozzles. These steps can be followed by a print test as described above.
Embodiments may have one or more of the following advantages. Soaking the printheads in a cleaning solution of n-methyl-2-pyrolidone and acetone for a limited period of time does not cause damage to the printheads, although the cleaning solution is an aggressive chemical. In particular, the cleaning solution does not dissolve the epoxy, which holds the printheads together because the cleaning solution is able to clean out the dried ink before dissolving the epoxy. Also, since the printheads merely soak in the cleaning solution, and the air used to flush the printheads is at a low pressure, the printheads are not subjected to high internal pressures which can damage the printheads. Soaking the printheads in the cleaning solution facilitates capillary action that draws the cleaning solution up into the blocked nozzle orifices. The capillary action of the soaking process of the present invention is an effective means of rewetting and re-dissolving the pigment/polymer plugs that can cause blockage of the printheads. The yield from the cleaning process is higher than that of conventional techniques. That is, of the printheads pulled from service to be cleaned, the cleaning process is able to clean a large percentage (over 90%) of the printheads so that they can be returned to service.